Inflammation, while generally beneficial, can cause considerable harm when over-activated, as is the case during sepsis. Our long-term goal is to characterize promising targets that are pivotal regulators of inflammation through which to intervene in excessive inflammatory responses. A post-translational mechanism of mounting significance in modulating inflammation is ectodomain shedding, a regulated proteolytic process that mediates the cleavage of cell surface proteins. Ectodomain shedding directs both instantaneous and prolonged alterations in the activity of various cytokines, cytokine receptors, and adhesion molecules. ADAM17 is a key membrane metalloprotease involved in ectodomain shedding;however, inactivating its gene in all cells of mice is lethal, and at this time little is known about ADAM17's biological functions in vivo. This represents an important knowledge gap in our understanding of the molecular events that regulate inflammation. We have generated ADAM17-null mice in which only the leukocytes lack functional ADAM17. These animals are viable, and, in studies with neutrophils and in vivo during inflammatory responses, we have reported ADAM17 to be a primary and non-redundant sheddase of several key inflammatory modulators, including the adhesion protein L-selectin, the pleiotropic cytokine TNF1, and TNF1's two receptors, TNFRI and TNFRII. We thus hypothesize that ADAM17 is a critical regulator of neutrophil recruitment and the ensuing inflammatory process during infection. Preliminary data in this application demonstrate that ADAM17 is regulated during neutrophil activation and apoptosis, and from a model of E. coli-mediated peritonitis we show that ADAM17 modulates neutrophil tissue infiltration, E. coli burden, and systemic levels of pro-inflammatory cytokines. Our objective in the proposed studies is to elucidate the mechanisms underlying ADAM17's role in neutrophil effector activities and the early stages of inflammation. In Aim 1, our investigative team will continue our evolving examination of the molecular processes involved in regulating ADAM17's activity by ascertaining the signaling events that induce the activation of ADAM17 during neutrophil apoptosis. In Aim 2, we will use ADAM17 null mice to directly examine the mechanisms by which ADAM17 promotes neutrophil accumulation and survival during E. coli-mediated peritonitis, focusing on neutrophil extravasation, apoptosis, and clearance. In Aim 3, we will establish ADAM17's contribution to the pathogenesis of E. coli-mediated systemic inflammation and neutrophil-mediated, host resistance to infection. Our novel mouse models of ADAM17- deficient leukocytes provide powerful, essential tools for studying ADAM17 in vivo, and the study's findings will greatly advance our understanding of the mechanisms underlying the regulation of ADAM17 and its role in modulating the inflammatory process and host resistance to Gram-negative bacterial infection. PUBLIC HEALTH RELEVANCE: The immune system's initial response to infection is inflammation, which, though generally beneficial, can be very harmful when over activated. We hypothesize that leukocyte ADAM17 plays a critical role in regulating inflammation and may serve as a promising drug target to prevent excessive inflammation. The overall goal of the proposed studies is to understand the influences of leukocyte ADAM17 on the early stages of the inflammatory response during infection.